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We read with great interest the paper by De Torres-Alba (1) on changes in the rate of pacemaker implantation after transition from the SAPIEN XT to the SAPIEN S3 transcatheter aortic valve (Edwards Lifesciences, Irvine, California). The investigators showed, in agreement with other reports, that the rate of pacemaker implantation is almost double with the SAPIEN S3 valve and that depth of implantation is associated with increased rate of permanent pacemaker placement (2–4).

We agree that the deeper the implantation of any device, the higher the risk for complete heart block and need for a pacemaker, given the proximity to the conduction system. This phenomenon seems to be more common with the S3 device, either because of its longer frame or because of its bulkier skirt. However, the accuracy and the magnitude of the association between depth and conduction disturbances as reported are debatable given the methods that were used for depth measurement.

Indeed, there may be flaws in the way implantation depth was estimated before prosthesis deployment and flaws in the way depth was measured after prosthesis deployment. As the investigators describe, 2 angiographic still frames were used to measure implantation depth: 1 pre- and 1 post-implantation. Before the prosthesis is deployed, the aortic annulus is seen in a coaxial projection, with the 3 cusps aligned. This projection is determined either by multislice computed tomography before the procedure or by aortography. The device is then positioned in the annulus, and once the desired depth is achieved, the device is deployed. After deployment, the device is not necessarily coaxial, so the projection is modified to obtain device coaxiality, and this is when final aortography is performed and depth is measured. In this modified projection, however, the aortic annulus is no longer coaxial. Proper localization of the hinge point between the device and sinus of Valsalva, and therefore proper implantation depth measurement, can be difficult in such circumstances and prone to parallax error (5). If the projection is modified significantly, 2 hinge points can be seen on the same side, making accurate measurements nearly impossible (Figure 1).

In this case, the projection has been modified after implantation, so the device appears coaxial. However, the annulus is no longer coaxial: 2 aortic cusps are seen at different levels on the septal side (arrows), making difficult the localization of the hinge point and therefore the measurement of depth of implantation.

Another issue is that of difference in orientation between the deployed device and the aortic annulus and root. This is illustrated by the difference in depth on the septal and nonseptal sides of the device. The investigators did not mention how they accounted for this phenomenon: averaging both measurements, recording only the largest measurement, or recording a measurement on only 1 side? The example provided in the figure suggests measurement of depth on the nonseptal side. Whether this is appropriate to assess a complication that arises in the septum seems counterintuitive.

Finally, the unit of measurement of depth, percentage of the prosthesis lying above the annulus, may also induce measurement error. Indeed, with this measurement unit, 2 patients with the same percentage depth of implantation but different device sizes would have different effective device length protruding in the left ventricle. This is because device height is different across sizes. For example, a patient with a 23-mm device with an implantation depth of 66.5% (i.e., the average depth of patients requiring pacemakers) would have 6.03 mm of the device in the left ventricle. Another patient with the same 66.5% implantation depth but a 29-mm device would have 7.54 mm of the device in the left ventricle. Although this 1.51 mm difference may seem trivial, it is actually larger than the difference in effective depth between patients requiring pacemakers and those not. For example, the average effective depth in patients with 29-mm devices requiring pacemakers is 7.54 mm, compared with 6.23 mm in those with the same device size but not requiring pacemakers, with a difference between groups of 1.31 mm on average.

To adequately measure device implantation depth, future studies should rely on post-procedural multislice computed tomography. This would allow measurement of depth all around the annulus, not only on the septal and nonseptal sides. The method described by De Torres-Alba et al. (1) and others could also be validated.

Footnotes

Please note: Dr. Lefèvre is a proctor for Edwards Lifesciences. Dr. Chevalier is a proctor for Medtronic. All other authors have reported that they have no relationships relevant to the contents of this paper to disclose. Drs. Sawaya and Spaziano contributed equally to this work.